Planar Contact with Solder

ABSTRACT

A method of fixing reflowable elements on electrical contacts. The method includes providing a strip having a number of electrical contacts, each contact including a contact body and a tail portion extending away from the contact body. The tail portions of the contacts are then disposed adjacent an elongate reflowable member. The elongate reflowable member is pushed onto the tail portions of the plurality of contacts. Subsequently, the elongate reflowable member is cut into a plurality of separate reflowable elements, each reflowable element corresponding to one of the tail portions. The electrical contacts with the reflowable element attached thereto are separated from the strip.

RELATED APPLICATION

This application is a divisional application claiming priority from U.S.non-provisional patent application Ser. No. 12/727,146 filed March 18,2010 and entitled “Planar Contact with Solder” which claims priorityfrom previously filed U.S. Provisional Patent Application Ser. No.61/161,231 filed on Mar. 18, 2009, also entitled “Planar Contact withSolder,” the benefit of which is hereby claimed under 35 U.S.C. §119(e)and incorporated herein by reference.

FIELD OF THE INVENTION

The present invention relates to electrical contacts for providing anelectrical connection between first and second electronic components,and more specifically relates to electrical is contacts having areflowable element disposed thereon.

BACKGROUND OF THE INVENTION

Electrical connectors are frequently attached to a substrate, such as aprinted circuit board (PCB), using a Ball Grid Array (BGA) type ofelectrical connection. The BGA includes a plurality of solder balls thatare used to connect electrical contacts of the connector to the PCB. Atypical BGA connector is connected to an array of electrical contactpads or traces disposed about the surface of the substrate. The solderballs are attached to the contact pads by first applying a resin flux tothe electrical contact pads, positioning the solder balls onto theelectrical contact pads, and running the connector through a reflowfurnace. During the reflow process the solder balls are held in positionby the flux and wetted onto the electrical contact pads. In addition toholding the solder balls in position, the flux promotes the wetting ofthe solder balls to the contact pads and chemically cleans the contactpad surfaces.

However, the small solder balls in a BGA connection produce only a shortconnection height between the electrical contacts of the connector andthe contact pads of the substrate. These short connections are subjectto high mechanical stress if any movement occurs between the connectorand the substrate. As a result, the connection between the connector andthe substrate is vulnerable to failing as a result of the solderconnection breaking due to stress.

One approach to apply solder balls on the contacts involves reflowingsolder, placing the liquid solder on the contact, and allowing thesolder to cool to form a ball disposed on the contact. However, this isa very complex and time consuming process. The requirement to heat andcool the solder as it is applied to the contacts can be time consuming.

BRIEF SUMMARY OF THE INVENTION

The present invention provides a method of fixing reflowable elements onelectrical contacts. The method includes providing a strip having aplurality of electrical contacts, each contact including a contact bodyand a tail portion extending away from the contact body. The tailportions of the plurality of contacts are then disposed adjacent anelongate reflowable member. The elongate reflowable member is pushedonto the tail portions of the plurality of contacts. Subsequently, theelongate reflowable member is cut into a plurality of separatereflowable elements, each reflowable element corresponding to one of thetail portions. The electrical contacts with the reflowable elementattached thereto are separated from the strip.

The present invention also provides a contact strip with a plurality ofelectrical contacts each having a reflowable element disposed on a tailportion of the contact. In one embodiment, the electrical contactincludes first and second legs disposed around an opening in thecontact.

BRIEF DESCRIPTION OF THE SEVERAL VIEWS OF THE DRAWINGS

Exemplary embodiments of the present invention will be described in thefollowing and are schematically shown in the drawings, in which:

FIG. 1 shows electrical contacts in accordance with an embodiment of thepresent invention attached to a strip;

FIGS. 2-4 show the tail portions of the electrical contacts of FIG. 1disposed adjacent an elongate reflowable member;

FIGS. 5 and 6 illustrate an embodiment of a method of attaching thereflowable member on the tail portions of FIG. 1;

FIG. 7 shows a rear view of the reflowable member and tail portions ofFIGS. 5 and 6 illustrating the connection between the reflowable memberand tail portions;

FIG. 8 shows a front view of the reflowable member and tail portions ofFIGS. 5-7 and cut lines of the reflowable member;

FIG. 9 shows the tail portions of FIG. 8 with cut reflowable elements;

FIGS. 10 and 11 illustrate an alternative embodiment of a method ofattaching the reflowable member to the tail portions;

FIG. 12 shows an alternative embodiment of the tail portions inaccordance with the present invention;

FIG. 13 shows the tail portions of FIG. 12 attached to an elongatereflowable member;

FIGS. 14 and 15 show additional embodiments of tail portions withreflowable elements attached thereto;

FIG. 16 shows a housing including electrical contacts with solderdisposed thereon;

FIG. 17 shows the housing and electrical contacts of FIG. 16 in thevicinity of a substrate with substrate contacts; and

FIG. 18 shows the electrical contacts electrically connected to thesubstrate contacts of FIG. 17.

DETAILED DESCRIPTION OF THE INVENTION

is This application is a divisional application claiming priority fromU.S. non-provisional patent application Ser. No. 12/727,146 filed Mar.18, 2010 and entitled “Planar Contact with Solder” which claims priorityfrom previously filed U.S. Provisional Patent Application Ser. No.61/161,231 filed on Mar. 18, 2009, also entitled “Planar Contact withSolder,” each of which is incorporated herein by reference for allpurposes.

FIG. 1 shows an embodiment of the present invention with two electricalcontacts 2 attached to a strip 4 of electrical contacts. Preferably, thecontact strip 4 is long and has a number of electrical contacts 2attached thereto. Each of the electrical contacts 2 has a contact body 6and a tail portion 8 extending from the contact body and typicallyextending in a direction away from the strip 4. Each electrical contact2 has one or more breakaway attachment points 10 to the contact strip 4.Thus, the electrical contacts 2 can be detached from the strip 4 andused individually. In the illustrated embodiment, the length of thestrip 4 is made up by a portion of the contact bodies 6 themselves. Inother words, the contact bodies 6 are attached directly together at theattachment points 10 and the series of attached contact bodies 6 definethe strip 4. Alternatively, the strip 4 can be a separate piece with thecontact bodies 6 attached thereto at the attachment points 10. The strip4 and the contacts 2 can be formed in a single plane, as shown inFIG. 1. For example, the contacts 2 and the strip can be stamped from asheet of metal or a metal foil. Planar contact strips can beadvantageous because of high reliability in their manufacture and lowproduction costs.

In use, the electrical contacts 2 serve to electrically connect firstand second electrical components. For example, the contact body 6 of theelectrical contact 2 can be held in a housing of the first electricalcomponent, such as an electrical connector or an electronic package, inelectrical communication with a terminal of the first component. Thetail portion 8 of the contact 2 extends out from the housing such that afree end 12 of the tail portion 8 is disposed at a remote end of thecontact 2 from the housing. The free end 12 of the tail portion 8 isconfigured to be electrically connected to a corresponding terminal ofthe second electrical component, such as a contact pad of a substrate.To form the attachment between the free end 12 of the tail portion 8 andthe contact pad, solder is used to mechanically bond and electricallyconnect the tail portion 8 and the contact pad. In accordance with thepresent invention, the reflowable material is disposed on the tailportion 8 of the contact in advance of connecting the electricalcomponents. Accordingly, the first component can be packaged andtransported with reflowable material disposed on its contacts. Moreover,the reflowable material can be placed on the contacts 2 before they aredisposed in the housing of the first electrical component.

In accordance with embodiments of the present invention, the reflowablematerial is disposed on the tail portions 8 of the contacts 2 by pushingthe reflowable material onto the contacts 2. Each of the tail portions 8include a holding section 14 that is adapted to hold the reflowablematerial on the contact once it has been pushed onto the tail portion 8.In the embodiment shown in FIG. 1, the holding section 14 includes twolegs 16 disposed on either side of a circular opening 18. After thereflowable material is pushed onto the holding section 14 of thecontacts, the feet 20 of each leg 16 help to securely retain thereflowable material on the tail portion 8. As described in more detailbelow, the reflowable material that is pushed through the opening 18 ispartially surrounded by the legs 16 and their respective feet 20ensuring that the reflowable material does not slip off the contacts 2.The feet 20 serve as a catch to hold the reflowable material in place bybeing wider than a central portion of the legs, which act as a narrowconnection. Thus, the reflowable material will not slip off the contact2 because the catch is wider than the narrow connection, which isdisposed on the tail portion 8 between the catch and the contact body 6.

An example of a reflowable material that is suitable with the presentinvention is solder. Solder can be used as the reflowable materialbecause it will reflow at elevated temperatures that are below themelting point of the contacts 2 and surrounding components. For example,depending on the particular material, solder can have a melting point ina range between 90° C. and 450° C. Accordingly, the solder can reflowand connect the contact 2 to a substrate terminal or contact pad withoutaltering or melting the contact 2, the substrate terminal, the substrateor any structural element near the solder, such as a housing holding thecontact 2. An exemplary suitable solder material is composed of amixture of tin and lead. Due to regulatory pressure to reduce the amountof lead used in electrical components, it may be advantageous to use alead-free solder. Examples of lead-free solders frequently include tincombined with other components such as copper, silver, bismuth, indium,zinc and antimony. Many suitable solders have a reflow temperature thatis below 220° C.

FIGS. 2-7 illustrate solder being pushed onto the electrical contacts 2of FIG. 1 from the side. In FIGS. 2 and 3 an elongate solder member 22is shown disposed in front of the electrical contacts 2. The illustratedelongate solder member 22 may be in the form of a solder wire with aflux core 24. As shown, the elongate solder member 22 is positioned soas to extend along an axis 26 that is offset from and parallel with theplane 28 of the contacts 2. The elongate solder member 22 is then pushedonto the contacts 2, as depicted by the motion arrow in FIG. 4, suchthat the axis 26 of the solder member 22 is aligned or nearly alignedwith the plane of the contacts 2. Alternatively, the contacts 2 can bepushed onto the solder member 22. As a result of the solder member beingpushed onto the contacts 2, a portion of the solder member 22 and theflux core 24 is inserted through the opening 18 in the holding section14 of the solder member. Accordingly, the feet 20 can hold a centralportion 30 of the solder that is disposed within the opening 18 andprevent the solder from slipping off the tail portion 8. To promote asecure connection between the contacts 2 and the solder member 22, theholding sections 14 are preferably sized to fit within the solder member22. The envelopment of the holding sections 14 within the solder member22 is aided by the parallel orientation of the axis of the solder member26 with the plane 28 of the contacts 2. However, the secure engagementbetween the holding section 14 and solder member 22 can be further aidedby making the features of the holding sections 14 small enough to fitwithin the solder member. For example, the diameter d of the opening 18may be smaller than the diameter of the solder member 22, shown in FIG.2. Moreover, the width W of the entire free end 12 of the tail portion 8can be smaller than the diameter D of the solder member. As a result,the entire holding section 14 can securely engage with the solder member22.

Depending on the malleability of the solder, parts of the solder may bepushed around the solder contacts 2 partially encompassing the legs andfeet, as shown in FIG. 7. By encompassing the legs 16 and feet 20 of thecontacts 2, the solder is less likely to be dislodged from itsconnection with the holding section 14 of the contact 2. Themalleability of the solder member 22 is partially determined by theconstituent material of the solder. In addition, the malleability of thesolder can be increased by raising its temperature. Accordingly, the actof pushing the solder member 22 onto the contacts 2 can be carried outat an elevated temperature. Thus, the solder member 22 will more easilybe pushed onto the tail portions 8 of the contacts 2 and will encompassthe legs 16 and feet 20 more readily. Preferably, the elevatedtemperature is above ambient temperature but below the reflowtemperature of the solder. For example, depending on the type of solderused, the solder member 22 can be pushed onto the contacts 2 at anelevated temperature that is substantially below 180° C.

With the solder member 22 disposed on the contacts 2, the solder can becut into individual solder elements 32, as shown in FIG. 9. For example,the solder member 22 can be cut along cut lines 34 shown in FIG. 8 toproduce the solder elements 32. Once the contacts 2 have individualsolder elements 32 disposed on their respective tail portions 8, theycan be used to connect a first electrical component, such as anelectronic package housing, to a substrate, such as a PCB. Accordingly,the individual contacts 2 are separated from the strip 4, disposed inthe housing and then connected to the substrate by reflowing the solder.Alternatively, the contacts 2 can be separated from the strip 4 beforethe solder member 22 is cut into the individual solder elements 32.

FIGS. 10 and 11 illustrate an alternative embodiment of a method ofattaching the solder member 22 to the contacts 2. In this embodiment,the solder member 22 is positioned along an axis 26 that issubstantially coplanar with a plane 28 of the contacts 2. The free ends12 of the contacts 2 are disposed adjacent a surface 36 of the soldermember 22 and the contacts 2 are pushed down into the solder member 22as shown in FIG. 10. In this embodiment, the contacts 2 are pushed alongthe direction of the plane 28. Alternatively, the solder member 22 canbe pushed onto the contacts 2 with the solder member 22 moving along thedirection of the plane 28. As a result, the holding section 14 of eachcontact 2 is disposed within the solder member 22, as shown in FIG. 11.The contact may be positioned so that the free end 12 is disposed withinthe middle of the solder or the free end can be coincident with thesurface of the solder member 22 at the side opposite insertion.Alternatively, the contact 2 may be pushed through the solder member 22sufficiently that the contact passes entirely through the solder member22 and a portion of the contact at the free end 12 extends out from thesolder member at the side opposite insertion. Preferably, themalleability of the solder member is great enough that some of thesolder material will move into the opening 18 disposed between the legs16 so that the solder can be held in place by the catch or feet 20. Oncethe solder member 22 is attached to the tail portions 8 of the contacts2, the solder can be cut along cut lines 34 into solder elements 32 in asimilar manner as described above with respect to FIG. 8. Again, thecontacts with solder elements 32 disposed thereon are used to connectfirst and second electrical components.

Another embodiment of contacts 2 in connection with the presentinvention are shown in FIGS. 12 and 13. These contacts have advantageousfeatures for the above-described method of pushing the free ends 12 ofthe contacts into the solder member 22. The contacts 2 shown in FIGS. 12and 13 have an arrowhead shape which facilitates easy insertion of thecontacts 2 into the solder member. The free end 12 of the contacts 2 isin the form of a point 38 which will enter into the solder member 22easily. From the point 38, the contact extends to a widened sectionincluding the two rear angles 40 of the arrowhead. A narrow connectionsection 42 connects the arrowhead to the rest of the tail portion 8 ofthe contact 2. In the illustrated embodiment, the holding portion 14 ofthe contact includes the arrowhead and the narrow connection section 42.Each of the rear angles 40 thereby act as a catch to hold the soldermember 22 onto the contacts. When the contacts are inserted into thesolder member 22, the solder material surrounds the narrow connectionsection 42 and the contacts are securely held in the solder material bythe catches or wide rear angles 40 of the arrowhead.

To facilitate even easier insertion into the solder member 22 and tocontrol solder reflow, part of the tail portions 8 can be covered with acoating or plating. For example, the insertion portion 14 of thecontacts 2 shown in FIG. 2 include a tin plating 44 on the surface ofthe contacts. The tin plating 44 helps direct the solder reflow to acorresponding contact, for example a solder pad on a substrate. Theportion of the contact 2 that does not include tin plating 44 is likelyto be subject to some corrosion. As a result that portion of the contactwithout tin plating 44 will be more resistant to adhesion of the solder.Accordingly, the solder will reflow onto the solder pad rather than wickup the contact 2.

The contacts can optionally include a stress or tension relief mechanismor spring element 46 that aids in relieving mechanical stress on thesolder when it is attached to a terminal such as a contact pad.Embodiments of such spring elements are shown in FIGS. 14 and 15.Generally, the tail portion 8 of each contact 2 in these embodiments canbe similar to the previously described embodiments and inserted into thesolder member 22, as described above. However, the contacts 2 includethe spring element 46 disposed between the contact body 6 and the freeend 12 of the contact. The spring element 46 can be part of the tailportion 8 or it can be a separate part of the contact 2. The springelement 46 is left outside of the solder member 22 when the tail portion8 is inserted therein. As a result, the spring element 46 is positionedbetween a solder attachment to a first electrical component and a secondelectrical component when the components are connected. Accordingly, themechanical stress caused by any slight movement between the electricalcomponents is absorbed by the spring element 46. The spring element 46can be formed by one or more bends 48 in the contact 2. Preferably, ifthe contacts are made from a sheet of metal or a foil, the bends aremade with respect to the plane of the sheet, as shown in FIG. 14. Theillustrated spring element 46 of FIG. 14 includes three bends 48 forminga pre-buckled contact. Alternatively, the spring element 46 can bestamped in the contacts, as shown in FIG. 15. For example, the springelement 46 can be provided by an undulated section 50 that is formedwhen the contact is stamped from a sheet of metal or a metal foil.

Once the solder elements 32 are disposed on the contacts 2, the contactscan be placed in a housing 52, for example, of an electronic package.The tail portion 8 of the contacts 2 extend out from the housing 52 withthe solder elements 32 disposed away from the housing 52 as shown inFIG. 16. To attach the contacts 2 to a second device 54, the housing 52is brought in the vicinity of the second device with the contacts 2adjacent respective corresponding contacts 56 of the second device. Inthe illustrated embodiment shown in FIG. 17, the second device 54 is asubstrate with solder pads 56 disposed thereon. The solder pads 56 caninclude a solder paste 58 disposed thereon to facilitate better adhesionbetween the contacts 2. The contacts 2 are then electrically attached tothe solder pads 56 by heating the solder elements 32 and causing them toreflow. When the solder hardens, a solder connection 60 is providedbetween each contact 2 and the respective solder pad 56.

Although the preferred form of the invention has been shown anddescribed, many features may be varied, as will readily be apparent tothose skilled in this art. It is the intention, therefore, to be limitedonly as indicated by the scope of the claims appended hereto.

What is claimed is:
 1. A method of fixing reflowable elements onelectrical contacts, the method comprising: providing a strip includinga plurality of electrical contacts, each contact including a contactbody and a tail portion extending away from the contact body; disposingeach tail portion of the plurality of electrical contacts adjacent anelongate reflowable member; moving the elongate reflowable member withrespect to the contacts, such that at least a part of each tail portionis inserted into the reflowable member; cutting the elongate reflowablemember into a plurality of separate reflowable elements, each reflowableelement corresponding to a respective tail portion; and separating theelectrical contacts from the strip.
 2. The method of claim 1, wherein:each of the tail portions includes a first leg and a second leg, whereinthe first and second legs are disposed on opposite sides of a centralopening of the tail portion, and wherein each leg includes a narrowconnection section and a foot that is wider than the narrow connectionsection.
 3. The method of claim 1, wherein each of the tail portionsincludes: an arrowhead shape, and a narrow connection portion disposedbetween the arrowhead shape and the contact body.
 4. The method of claim1, further comprising: bringing each of the electrical contacts adjacentto a respective corresponding contact of a device; and adhering eachelectrical contact to the corresponding contact of the device, whereinthe adhering is accomplished by: elevating an ambient temperature to atemperature that is greater than a melting point of each of thereflowable elements, but less than a melting point of the electricalcontacts, and less than a melting point of the contacts of the device.